Says one approach was 'a mistake' even as users struggle to stop the OS from installing.

He has confirmed, for instance, that if one "reserves" an upgrade with the Get Windows 10 applet, then cancels the reservation, Microsoft will at some point revert the machine to its original reserve-a-copy state. "Even though it's possible to cancel your Windows 10 upgrade reservation in the Get Windows 10 app, doing so appears to put your computer in a state where it can actually download Windows 10 as a Windows Update," Mayfield wrote in a long blog post.

The owner of this PC can't get to the usual Windows Update panel that shows other updates, and may believe the only option is to upgrade to Windows 10. Credit: Jim Feltner

Mayfield theorized that those who are seeing the most aggressive messages in Windows Update or in separate dialogs were people who had at one time reserved a copy, then canceled that reservation. "The moment you click [to reserve an ungrade], you put the PC on a path to upgrading to Windows 10," he said in the interview, even if the reservation was subsequently canceled.

The most likely reason for that odd behavior, said Mayfield, was Microsoft's redistribution of some updates. "Microsoft has started to reissue some specific update patches, even if you already installed them before," Mayfield observed. Among them: the original Get Windows 10 applet update (identified by Microsoft as KB3035583), or perhaps this one from last week.

Mayfield's best guess was that follow-up updates to KB3035583 -- which was, in fact, revised as recently as Sept. 24 -- "flipped the bit" on the PC's status vis-a-vis Windows 10 upgrade eligibility. "I think they may be doing doing this to get [the update] onto PCs that have just been reformatted, or on new PCs," Mayfield said.

One of the eight Windows 7 or 8.1 machines Mayfield uses as his test bed reverted to a good-to-go-on-Windows-10 state in this fashion.

"[This] is our first evidence that Microsoft can change some of these settings via Windows Update," said Mayfield.

A surge in interest for GWX Control

While Mayfield didn't have answers to every Computerworld question about the Windows 10 upgrade behavior he's seen, he knew one thing, if only because of a major increase in traffic to his website and a big bump in downloads of GWX Control Panel. "Something happened this week," Mayfield. "Downloads and traffic at my site have exploded in the past couple of days, even though my program's been around and sort of known for over a month."

The number of GWX Control Panel downloads jumped eight-fold Wednesday, said Mayfield, and the site traffic increase was even larger. The most likely reason: Microsoft pre-checking the Upgrade to Windows 10 optional item in Windows Update.